The present invention relates to a stream communication system in which there is transferred an encoding stream for which real time mode of operation is required as in video, audio and the like and particularly, to a stream communication system and a stream transfer control method for automatically controlling parameters relating to stream transfer following load variations by a feed back system while giving consideration to a quality of a transfer stream.
In company with progress in a computer network technology and a communication technology for digital information, a communication system has, in recent years, been developed; the communication system is called a stream communication system, in which there is handled a multimedia stream represented by an encoding image stream, an encoding image stream including speech information and the like, in other words a real time stream which requires real time mode of operation.
There are known methods by which real time transfer adopted in communication systems of this kind is maintained.
A first method is to adjust a sending data volume by annulling (discarding) part of data in a stream, but there is a fear in the first method that important part is lost.
A second method is to execute stationary filtering processing based on data priorities and to maintain real time transfer while keeping back as much important part of the data as possible. As a concrete example of the second method, there has been known a method in which several levels (data priorities) are provided by picture types in a system in which a MPEG (Moving Picture Experts Group) video stream is handled. This method has a feature that there are executed rate control by stepwise specification including transfer of all data, annulment (discard) of B picture, annulment of B, P pictures and annulment of all video (transfer of audio only). According to this method, for example in a situation where transfer of all data cannot be continued, even one frame of the B picture cannot be transferred. In other words, since the second method adopts an extremely discrete rate control and besides a transmission rate is not constant, real time transfer is not to be maintained while keeping a quality at a highest level attainable in the second method.
As described above, methods which have conventionally been known in which real time transfer is maintained (the first and second methods) are not to dynamically adjust a transmission data volume while giving consideration to a stream quality in real time transfer of a multimedia stream (encoding stream) and a transmission rate cannot, accordingly, be specified.
A third method is to reserve a network band (transmission rate) in advance of performing steam transfer and thereby guarantee QoS (Quality of Service). In the third method, however, it is only judged whether or not a reservation is allowed and when there is no room in the band for use, no reservation is allowed and no transmission can thus be performed. This means to restrict the number of users and no control is performed in such a manner that there is attained a band as close to the user""s desirable band as possible.
It is an object of the present invention to provide a stream communication system and a stream transfer control method in which dynamic adjustment of a transmission rate is enabled while not only is real time mode of operation maintained, but a quality is also maintained at a highest level attainable, even when load variations arise, by processing in which the load variations in a network or a system is fed back to an upstream side, the load variations is followed on the upstream side and a transmission data volume is decreased through automatic annulment of data part with a lower priority.
It is another object of the present invention to provide a stream communication system and a stream transfer control method in which a further feed back control is not applied in a time period of a transition state from starting of adjustment of a transmission rate till a requested transmission rate is attained and thereby a system is, with certainty, prevented from becoming unstable.
In order to solve the above problems, the inventor has proposed a method in which a dynamic quality control is enabled by not performing a discrete rate control but a continuous rate control. In this method, a packet with a lower priority (lower degree of importance) in a stream is positively annulled (discarded), and thereby a quality and a transmission rate are both adjusted, whereby an available transmission rate (transfer band) can be made to be as close to a transmission rate specified by a user as possible, while maintaining a quality at a highest level attainable.
The above described methods, however, give no consideration to variations of a load state of a network or a system and there are performed neither quality adjustment nor transmission rate adjustment which is most suitable for the load state. For this reason, it is difficult to maintain a transmission rate which a user specifies in a situation where a load state of a network or a system varies. Real time image stream transfer being taken up as an example, data transfer is generally performed while maintaining a bit rate (encoding rate, content rate) of a content. At this time, when a packet loss arises since a network band is not sufficiently secured or when decode processing of reception data is insufficiently performed due to shortage of a processing capability at a terminal, an image presented to a user is deteriorated in quality.
Therefore, the present invention has (claim 1).
As a feature, in such a constitution, a parameter showing a transmission rate at which there is enabled real time transfer at a control target node is calculated at a node which is assigned with a role as a management node corresponding to the control target node and at least one node located on the downstream side from the control target node which is assigned with a role as a monitoring target node, based on information showing a load state of the at least one node which is notified from (internal state notification means of) the at least one node and on information showing a transmission rate set currently at the control target node, and the parameter is fed back to the control target node. Thereby, at the control target node, there is performed a stream shaping processing in which data part with a lower priority is automatically annulled in order to decrease a data volume, while a less transmission permissible priority is given stepwise and the number of transmission permissible data blocks with the same priority as the transmission permissible priority in the same cycle is increased stepwise so that an actual transmission rate is changed to a new transmission rate shown by the parameter fed back from a current transmission rate.
As a result, even if there are load variations in a network or a system, dynamic adjustment of a transmission rate can be performed while maintaining not only real time mode of operation but a quality at a highest level attainable.
According to (claim 2), feed back control with higher precision can be realized. In the constitution (claim 2-1), it is recommended that at least one module in which a data processing result can be calculated, among modules constituting a monitoring target node, is assigned with a role as a monitoring target module and a node load is judged from a module load obtained from data processing results at all the monitoring target modules in the monitoring target node.
Periodicity in a data structure can be detected with no stream analysis with complexity by adopting a constitution in which there is used an encoding stream in which transmission control reference information as a standard for transfer control is inserted and a transmission permissible priority is updated based on a transmission result in a previous cycle for each cycle when judgment is performed based on the transfer control standard information.
It is recommended that a specified algorithm, that is an algorithm of (claim 5), is adopted for stream shaping processing in stream conversion means.
There can be realized a continuous rate control by which there is achieved an actual transmission rate as close to a specified one as possible while there is transmitted a data block with a highest priority attainable by applying the algorithm and while a relation between a transmission and a quality is clearly maintained.
The present invention has (claim 6).
As a feature, in such a constitution, since in a period of time of a transition state from the time when adjustment of a transmission rate gets started at a control target node according to feed back from a management node till the time when an actual transmission rate reaches to a requested one, feed back control in the management code is stopped according to a transition state starting notification message transmitted from a control target node when the rate adjustment gets started, there is applied no further feed back control to the control target node by the management node in the transition state period of time and it is sure to be prevented from occurring that a system gets unstable.
In a period of time of a non-transition state, that is a period of time of a steady state, since internal state notification messages, each including a parameter which shows a current transmission rate, are transmitted at regular intervals to a management node from stream conversion means of a control target node, a parameter showing a latest transmission rate set at the control target node can constantly be achieved by the management node, whereby feed back with high precision can be performed.
The present invention has a constitution, as a feature, that a plurality of data reception results notified to a management node from a monitoring target node are, in the order of a time series, held in a data reception results buffer adopting a first-in, first-out way and the plurality of data reception results in the buffer are respectively modified by weights in a corresponding manner to the order thereof and an average of the data reception results after the weighing is compared with an upper bound threshold and a lower bound threshold corresponding to a permissible reception rate range which is determined by a transmission rate set currently at control target node and link load results are output in three levels composed of Link Load: Large, Link Load: Proper and Link Load: Small based on the comparison results.
In such a constitution, there is realized load judgment in which a change of link load over time is considered. This constitution can be applied to a module load and a node load as well.
The present invention has a constitution, as a feature, that, since a latest link load judgment result and a latest node load judgment result are stored in latest judgment result holding means, while there is prepared, in advance, matrix table information in which there is written a relation between combinations of all link load judgment results and all node load judgment results, both conceivable in advance, and judgment results in which a control policy for a corresponding control target node is indicated by three levels composed of xe2x80x9cTransmission Rate: Increasedxe2x80x9d, xe2x80x9cTransmission Rate: Unchangedxe2x80x9d and xe2x80x9cTransmission Rate: Decreasedxe2x80x9d, only if the matrix table information is referred to based on the combinations of a latest link load judgment result and a latest node load judgment result, a judgment result indicating a control policy for the corresponding control target node can be obtained with ease.
It is recommended that the present invention has a constitution which comprises: a judgment result buffer adopting a first-in, first-out way for storing judgment results, showing the obtained control policy, of n times in the past in the order of a time series; judgment result correction means for correcting a latest judgment result based on continuous judgment results of m times (mxe2x89xa6n ) in the past including the latest judgment result in the judgment result buffer when the latest judgment result is stored in the judgment result buffer; and window setting means for setting a window width indicating a value of the m (for example, according to the latest judgment result). Here, it is recommended that if all the judgment results of m times in the past are either xe2x80x9cTransmission Rate: Increasedxe2x80x9d or xe2x80x9cTransmission Rate: Decreasedxe2x80x9d, the latest judgment result is output with no correction, if all are xe2x80x9cTransmission Rate: Unchangedxe2x80x9d, the latest judgment result is changed from xe2x80x9cTransmission Rate: Unchangedxe2x80x9d to xe2x80x9cTransmission Rate: Increasedxe2x80x9d and then output and if different judgment results are mixed, xe2x80x9cTransmission Rate: Unchangedxe2x80x9d is output regardless of the latest results.
In such a constitution, it is possible to suppress a excessive reaction to pulse-like load variations.
It is recommended that the present invention has a constitution that the feed back control means is provided with transmission rate control range setting means for setting a minimum transmission rate and a maximum transmission rate which shows a control range for a transmission rate according to specification from outside, and when a transmission rate shown by the calculated parameter exceeds the maximum transmission rate, an actual transmission rate is changed to a parameter showing the maximum transmission rate, while when less than the minimum transmission rate, a stream transfer is stopped or an actual transmission rate is changed to a parameter showing the minimum transmission rate and a stream transfer is continued. (claim 15) At this point, it is recommended that the feed back control means is further provided with control mode setting means for setting control modes, according to specification from outside, which specifies so that when a transmission rate shown by the calculated parameter is less than the minimum transmission rate, stream transfer is stopped, or stream transfer is continued changing an actual transmission rate to a parameter showing the minimum transmission rate.
In such a constitution, it is possible to reflect a user""s desire on transmission rate adjustment and a control policy for quality adjustment and thereby, there can be realized stream transfer within a range of a cost and a quality desired by a user.
The present invention has a constitution, as a feature, that any of the plurality of nodes except a transmission node (sender node) can be assigned not only with a role as a monitoring target node, but with a role as only one management node for the monitoring target nodes, while a node at the front stage is assigned with a role as only one control target node for the management node.
In such a constitution, each node other than the transmission node in a system works as a management node for a node at the front stage and feed back control (QoS judgment) of the stream transfer section in the system can be performed in a distributed manner.
In the present invention, one of the plurality of nodes is assigned with a role as a management node.
In such a constitution, one node in a system can centrally perform load judgment (QoS judgment) of all the stream transfer system in the system and feed back control (QoS control) based on the judgment results.
As described above, according to the present invention, load variations in a network or a system are fed back from a management node to a control target node on the upstream side and data part with a low priority is automatically annulled whereby a transmission data volume is decreased, while a less transmission permissible priority is given stepwise following the load variations in the control target node and the number of transmission permissible data blocks with the same priority as the transmission permissible priority in the same cycle is increased stepwise. Hence, even if load variations occur, not only is real time mode of operation realized, but a quality is maintained at a highest level attainable, whereby dynamic adjustment of a transmission rate can be performed.
Besides, according to the present invention, in a period of time of a transition state from the time when the dynamic adjustment of a transmission rate gets started at a control target node following feed back from a management node till the time when a required transmission rate is reached, since feed back control in the management node is stopped according to a transition state starting notification message transmitted from the control target node when the rate adjustment gets started, further feed back control by the management node is not overlapped on the control target node and thereby the system is, with. certainty, prevented from being unstable in the transition state period of time.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.